Radio antenna



Oct. 27, 1942. L, TT 2,299,785

RADIO ANTENNA Filed May 16, 1940 2 Sheets-Sheet 1 Twcwzys Oct. 27, 1942.BARRETT 2,299,785

RADIO ANTENNA Filed May 16, 1940 2 Sheets-Sheet 2 L 4 0, L3. Vi 10/ iRADIO 857' (/ITTo Qugys Patented Oct. 27, 1942 RADIO ANTENNA Edward L.Barrett,

corporation of La Grange, 111., Barrett Engineering Company, Ch

Illinois assignor to lease, 111., a

Application May 18, 1940, Serial No. 335,589

18 Claims.

The invention relates to radio antennas, devices embodying the presentinvention being particularly adapted to meet the exigencies of use inautomobile installations.

One object of the present invention is to provide an antenna embodying aplurality of elongated tubular elements telescoped one on the other,together with a novel motor actuated arrangement for projecting andretracting the same.

Another object is to provide a radio antenna of the type embodying aplurality of telescoped tubular elements in which the problem oftransmitting the forces (from a motive power source) requisite forprojecting and retracting the tubular elements, is solved by utilizingas a transmission element a tightly spiraled wire helix led through thetubes and hidden from view in them, the wire helix being suflicientlyflexible to be coiled up in a small space when drawn in to retract theantenna, and yet sufliciently stifl to withstand without buckling thecompression forces applied to it when pushed outward to project theantenna.

Another object is to provide a novel drive mechanism suitable for use inan antenna of the character indicated in which a motion transmissionmember, in the form of a laterally flexible tightly spiraled helix ofwire, is threaded in the tapped interior of a hollow motor shaft so asto form a direct driven-screw connection with it, thereby obviating thenecessity of a speed-reduction gearing or other connecting elementsbetween the motor and the transmission element.

Another object is to provide a motor driven antenna of the typeindicated embodying a novel control arrangement for automaticallycorrelating the operation of the antenna projecting and retracting drivewith the operation of the radio set.

Another object is to provide a radio antenna embodying power actuatedmeans for projecting and retracting it and which is characterizedparticularly by its low cost and simplicity of construction, as well asits safety and ease of operation,

Still another object of the invention is to provide a motor drivenantenna having an extremely low capacity coupling with ground from itsvarious actuating parts, together with a high leakage resistance toground.

A further object is to afford an antenna of the type indicated having anactuating mechanism form as to make possible complete and adequateshielding w e still retaining small overall dimensions for the entireapparatus.

The invention also resides in various improvements and simplificationsin the construction of the power actuating and control switcharrangement for the antenna by means of which low cost and eiiiciency ofoperation are combined.

Further objects and advantages of the invention will become apparent asthe following description proceeds, taken in connection with theaccompanying drawings, in which:

Figure 1 is a fragmentary view of an automobile fltted with an antennaembodying the present invention.

Fig. 2 is a side elevation, with a portion broken away, of the antennaapparatus.

Fig. 3 is a longitudinal sectional view of the tensible wave-receivingstructure of the antenna, shown in substantially retracted position.

Fig. 4 is an enlarged vertical sectional view taken substantially alongthe line 4-4 in Fig. 2.

Fig. 5 is a longitudinal sectional view of the antenna actuatingmechanism, with the flexible transmission element partially reeled outrather than fully reeled out as in Fig. 6.

Fig. 6 is a detail sectional view of the takeup mechanism showing thetail end of the flexible transmission element when it is fully reeledout.

Fig. 7 is a transverse sectional view along the line in Fig. 5.

Fig. 8 is a detail perspective view of a drive bushing included in thepower actuating mechanism of the antenna.

Fig. 9 is a schematic wiring diagram of the control system for theantenna actuating mech anism,

Fig. 10 is a sectional view, similar to Fig. 6, of a modified form oftake-up container.

Fig, 11 is a schematic wiring diagram of a modified form of controlsystem.

While the invention is susceptible of various modifications andalternative constructions, I have shown in the drawings and will hereindescribe in detail the preferred embodiment, but it is to beunderstoodthat I do not intend to limit the invention but intend tocover all modifications and alternative arrangements falling within thespirit and scope of the invention as expressed in the appended claims.

Referring more particularly to the drawings,

whichis sufllclently compact and of such general the invention has beenshown herein as embodied in an automobile installation (see Fig. 1). Insuch an installation the antenna is exposed to extreme variations intemperature, and to rain, sleet, snow, and'the like, as well as tostrong vibrations and jouncing. Furthermore, in the event that theelectric actuating motor 1 for the antenna is driven from theconventional storage battery in the car, and that is the only convenientsource of current for such a motor, it must be capable of operationdespite extremely wide variations in voltage of, for example, 50% aboveto 50% below normal, such as are frequently encountered in the output ofconventional storage battery systems of automobiles. Although thepresently disclosed antenna is expressly adapted to meet theexigenciesof such an environment, as will more fully appear below, it is manifestthat antennas embodying my invention may also be used in a variety ofother installations.

In general, the antenna of Fig. i'comprises an extensible wave-receivingstructure It and an actuating mechanism, housed in a casing II, forprojecting and retracting the same. The casing II is desirably mountedin the rear portion of the well of a front fender I! on the car, asindicated, so that it is completely hidden from view, yet occupies anotherwise waste space so that it neither mars the appearance of the carnor interferes with its other parts. when the antenna is retracted itextends only a few inches above the surface of the fender so that itspresence is practically unnoticeable. On the other hand, when theantenna is projected to the operating position shown in Fig. 1, itaffords an ample length of wave-receiving structure, free of the carbodyso that it functions without interference or shielding from the car.As is hereinafter described in greater detail, the actuating mechanismhoused in the casing II is controlled from the interior of the car sothat the user need not manually pull the antenna out or retract it, or,in fact, give any spect to the 'outer tube II. The collar l8 isfashioned in the form of a flanged cup with an open bottom so that itconstitutes a stop for the inner end of the tube ID.

The rod II has on it an enlarged head ll of decorative shape which formsa stop connection between it and the tube [5. The outermost section ortube I1 is stationarily mounted in an insulating bushing I8 (Fig. 4)fixed within a threaded sleeve or bushing 19.

with the arrangement of telescoping elements described above, the entireseries can be projected or retracted by correspondingly pushing orpulling on the rod l4. Thus, to retract the wavereceiving structure, therod I4 is pulled inward until its head ll strikes the nose of the tubeI5. Thereafter continued inward motion of the rod It brings the tube I!with it and when the latter's inner end strikes the cup l8 on the tubeIt the latter is also drawn inward, the retractive motion of thesections l4, I5 and I6 being continued until they are withdrawn almostcompletely within the outermost tube I I in the final position shown inFig. 2. Similarly, to extend the wave-receiving structure, the rod I4 isthrust longitudinally outward. After' the rod It has been moved toproject a major portion of its length from tube IS, the enlarged innerend por-.- tion ll on the rod (see Figs. 3 and 4) strikes the neckedportion li of the tube [5, thereby drawing this tube outward with it.Next the collar 15 on the tube l5 engages the neck l6 on the tube It sothat the latter tube is moved on outward. The outward sliding motion ofthe tube It is finally limited, to prevent complete separation of thesections, by engagement of its collar It with the neck I I on the tubeH.

To form a concealed motion transmission con- I nection between thehereinafter described power special attention at all to the antenna.This unitary assembly or construction of the antenna permits it to beeasily handled and attached as a unit, thereby greatly simplifying itsinstallation, servicing and merchandising.

The wave-receiving structure It is made up of a series of telescopingelements or sections including, as the innermost, a slender, stainlesssteel rod 14 (Figs. 2, 3 and 4). Telescoped over this rod and on eachother are the next successive sections, in the form of seamless brasstubes I5, |6 and l1. Each of the tubes l5, l6 and i1 is necked in at itsouter end, as indicated respectively at l5, l6 and [1 in Fig. 3, to forma snug sliding fit with the next adjacent one of the telescopingelements. To aid freedom of movement the sliding surfaces arecustomarily oiled but in case of very cold weather when such oil becomessticky or in the event that the antenna becomes coated with sleet orice, it will be appreciated that the force required in projecting andretracting the telescoping sections is greatly increased andconsequently any drive mechanism for them must be able to take care of,without loss of efficiency, such heavy loads.

To guide the telescoping sections against side sway, collars I5 and Illare fixed tothe tube l5, respectively, at its inner end and at anintermediate point so as to space its inner portion from the encirclingtube It. Similarly spaced collars l6 and 5 are fixed respectively to theinner end and to an intermediate portion of the I tube It so as to guideits inner portion with reactuator in the casing H and the telescopingsections of the wave-receiving structure I0, I utilize a slender,flexible member I9 led up through the nested tubes l5, l6 and I1 andanchored to the butt end of the rod I4 (Figs. 3 and 4). This member l9must meet a number of peculiar, and in some respects antithetical,requirements. First of all it mustbe flexible enough to permit its beingcoiled or reeled up in a compact storage space when the antenna isretracted. Also it must be capable of transmitting sufficient tension toeffect retraction of the telescoping elements. 0n the other hand, themember I9 must be rigid enough that it can transmit sufficientcompression, without buckling, to project the telescoping elements evenwhen their sliding surfaces are sticky or heavily loaded. It should beobserved that buckling of the member l9 must be avoided not only becauseit might cause jamming of the cooperating driving parts but also becausesuch buckling would cause the member to rub against the side walls ofthe encircling tubes, this added friction drag thereby increasing evenfurther the compression load on the member I9. I have found that amember suitable to meet the requirements noted may be made by fashioninga tightly spiraled helix of tinned piano wire. This wire is spiraled sotightly that its adjacent convolutions are abutting and may, forexample, in the particular mechanism shown, be 0.025 inch piano wirespiraled in a helix of 0.078 inch outside diameter. This optimum ratioof about yet has the necessary characteristics of stiffness when woundin the configuration noted. The use of tinned wire is desirable becauseof the marked reduction in friction which such a finish accomplishes inthe event that the wire helix is threaded in a tapped driving bushing,as is the case in the hereinafter described actuator mechanism.

In accordance with another aspect of my invention an electric motor typeof actuating mechanism is provided such that the wire helix I9constitutes the driven element of a speed-reduction screw drive. Inother words, the convolutions of wire are themselves used as screwthreads. This provides, at very low cost, a long member which is ineffect screw threaded and which is of very desirable character, evenaside from the standpoint of economy, because it can so readily becoiled down in such a small space when reeled in for retraction of theantenna.

In the instant construction the actuator mech anism comprises anelectric motor designated generally at 20. (Figs. 4 and 5) having astator 2| and rotor 22. Desirably the motor 20 is adapted to operate ona direct current of low voltage so that it can be supplied from theconventional six volt storage battery of an automobile. The armature 22is carried by a shaft including an outer tubular steel jacket 23journaled in self-alining, self-oiling bearings 24 of well known formand which are mounted in the motor casing 25. The motor 20, being of thedirect current type, alsoincludes the usual commutator 26 and brushes21. This motor has stator or field windings 2I and an armature winding22, the motor being reversible by changing the relative polarity ofpotential supplied to the rotor and stator windings, respectively.

In order to form a drive connection, of the general character indicatedabove, between the motor and the flexible wire helix I9,- the latter isled through the hollow motor shaft and the latter is constructed topresent interior screw threads mating with the convolutions of the helixI9. In this manner the convolutions of the wire helix are themselvesused with screw threads so that the member I 9, which is fixed at itstail end to hold it against rotation, constitutes a driven screw whichis moved lengthwise by rotation of the motor shaft, the direction ofaxial movement for the member I9 depending of course upon the directionof motor rotation. For this purpose a tapped or interiorly threadedbushing 28 (Fig. 5) is fixed in the tubular shaft jacket 23 and the wirehelix or shaft I9 is threaded in it. Desirably the bushing 28 is made ofhard bronze and its exterior is circumferentially grooved and knurled(see Fig. 8). The tapped bushing 28 is iorce fitted in an insulatingbushing or sleeve 29 i Fig. 5) which is in turn force fitted in thetubular shaft jacket 23. The roughened exterior of the tapped bushing 28insures it against rotation with respect to the insulating sleeve 29. Itwill be observed that the longitudinal bore in the sleeve 29 is taperedoutwardly toward its respective ends, from the ends of the tappedbushing 28, so as to insure clearance from the helix i9. At therespective ends of the sleev 29 additional bushings of electricalinsulating material are forced in the ends of the motor shaft jacket 23.The sores in these bushings are tapered inwardly so as to form guidethroats loosely engaging the member I9 which passes through them. Itshould also be noted that the outer ends of the bushings 39 are turnedoutwardly to form oil-thrower surfaces which will, by centrifugal force,throw out any oil or other liquid falling on them and thus prevent itsentry into the interior of the motor shaft.

The novel screw type drive effects, with high emciency, a large speedreduction, without the necessity of interposing expensive and noisyspeed-reduction gearing. By way of example, if the helix I9 ha fortyturns per inch and the motor 20 revolves at 2.000 R. P. M. the speedreduction is great enough to require ten or twelve seconds to project orretract the antenna, a nice speed for the purpose. The high efficiencyof the drive connection, which is about per cent, results in a largemeasure from the minimization of friction between the drive bushing 28and the helix I9. To minimize this friction, the bushing threads are cutwith a special tap which shapes them to conform with the rounded crosssection of the outer sides of the helix turns which mesh with them. Thetinned finish 0n the helix I9, heretofore noted, also materially reducesthe friction. Still another factor in the minimization of friction isthe small length of the drive bushing 28. In the present instance it isonly long enough to mesh with about nine convolutions of the helix I9.

Despite the high efficiency and low friction noted just above, the driveis highly resistant to reverse operation. In other words, it ispractically impossible to rotate the bushing 28 as a driven member bypushing endwise on the helix I9 as a driver. Incidentally, this type ofreversal is, of course, to be distinguished from a mere reversal ofdirection of motion for the parts in which the bushing 28 still remainsthe driver and the helix I 9 the driven member. The latter type ofreversal is readily accommodated by the present drive mechanism.Inability of the helix I9 to perform as a driver in the system is ahighly necessary characteristic since the jouncing and vibration of anautomobile tends to cause the telescoped sections of the antenna to moveinadvertentiy to collapsed position. As will hereinafter appear,however, the switching arrangement of the present antenna is such thatthe antenna is automatically grounded and, hence, rendered inoperative,as soon as the retraction motion of the helix I9 starts. Hence, if thedrive connection permitted even a small endwise creep of the helix underthe conditions noted, the antenna would become grounded, so it isimperative that the driv should automatically lock against reversal ofthe driving and driven elements. 01 the common forms of drive available,as distinguished from the novel one herein disclosed, about the only onewhich has such a locking characteristic is a worm and worm wheel drive.In it, however, the eificiency is only about 20 per cent. This verygreat reduction in efficiency, as compared to 35 per cent for the hereindisclosed drive, is extremely bad in an installation of this typebecause either an almost prohibitively large and expensive electricdrive motor must be used or else the system will stall under overloadsencountered in cold or bad weather conditions or when the supply voltagefrom the automobile storage battery becomes low.

The casing ll not only houses the motor 20 described above, and itsassociated control switches hereinafter described, and electricallyshields the various parts housed in it, but also forms a take-up chamber3| (Fig. 5) into which the fiexible wire helix I9 is coiled when thewavereceiving structure I 0 is retracted. To this end the casingcomprises a tubular sheet metal body portion 32 in the intermediateportion of which the motor casing 25 is fixed. The opposite ends of thebody 32 are closed by removable sheet metal caps 33 and 35. To theouterend cap 33 (see Fig. 4) is fixed the threaded mounting bushing l9.To'secure the unitary antenna structure in place on an automobilefender, as shown in Fig. l, the bushing i9 is projected through asuitable hole M on the fender l2 (Fig. 2) and lock nuts 35 are threadedon the bushing, holding the assembly in place with the casing ii hiddenbeneath the panel or fender and with the wavereceiving structure itprojecting freely from the other side.

At its inner end the casing it presents the generally cylindricaltake-up chamber 35 to the adjacent end of the hollow motor shaft andfrom which end of the motor shaft the flexible wire helix i9 emerges asthe telescoping antenna elements are retracted. Means is provided foranchoring the inner end of the helix 19 in the chamber 39 so as torestrain the helix against rotation, as is necessary for properoperation of the drive, also to hold its inner end portion permanentlycurled in a direction generally circumferential of the chamber 36. Forthis purpose the end of the helix It is soldered to the free end of aleaf spring '36, anchored to the casing cap 341 as described below, withthe helix is extending laterally from the spring 36. It will thus beseen that when a maximum permissible amount of the helix is pulled outof the take-up chamber 36 the remaining tail end portion is curled asshown in Figs. 6 and 7. Hence, when the helix it is fed into the chamber3!, this initial curl will cause it to coil up neatly and automaticallyin the chamber without the necessity of providing any take-up reel orthe like. The omission of a take-up reel makes possible not only theaccomplishment of an important saving in cost but in addition verysubstantially reduces the capacity coupling to ground for the antenna.As to the latter point it should be noted that if a metal take-up reelis used for the helix E9 or,

similar element the take-up reel must be of the same potential as theantenna element to which it is connected, namely, the helix l9, andhence the entire surface of the take-up reel adds to the capacitycoupling to ground.

In order to prevent the electric driving motor 26 from causingundesirable interference noises to issue from the speaker of theassociated radio set when the antenna described is used on a radioreceiver, a muting switch is provided for automatically silencing theset whenever the motor 29 is in operation. In the embodiment of theinvention shown in Figs. 1 to 9, inclusive, this muting switch comprises(see particularly Fig. 6) astationary contact 31 and a cooperatingmovable contact 38 fixed to the mid-portion of the leaf spring 36. Thebutt end of the leaf spring is fixed to an insulator supporting block 39by an overlying insulator block Ml (see also Fig. 7). Hence when theswitch contacts 3?, 38 are open the extensible antenna, which isdirectly connected to the spring 35 as described, is isolated fromground. On the other hand, when the contacts 31, 38 are closed, theantenna structure is connected to ground through them, or in otherwords, is grounded to the housing H and the automobile body. Suchconnection of the an- -tenna to ground of course mutes or silences theradio receiving set. Since the leaf spring 36 is attached to the tail ofthe flexible wire helix IS the contacts 31, 38 are pulled open by thetension exerted by the helix I 9 just as the telescoping 7 antennasections reach their fully extended position. It will be observed,however, that whenever the motor 2&3 is running to feed the flexiblehelix l9 into the chamber 3! or to draw it out of the same, there willbe a sumcient slack length of the helix in the chamber so that thespring 86 retains the contacts 37, as closed. In other words, the switchmechanism described acts auto= matically to mute the associatedreceiving set whenever the antenna actuating motor is in operation,- butautomatically removes the muting round connection for the antenna whenthe latter is fully extended. 1

For the establishment of a circuit from the antenna wave-receivingstructure it to an ,associated radio set, a bayonet type plug receptacleM is provided (see Fig. 4). This receptacle is fixed in the side wall ofthe casing H and is connected through a conductor di with the outermostsectionill of the telescoping sections. A suitable plug connector (notshown) may of course be inserted into the receptacle M to complete theconnection to the in-put terminal of the radio set. Similarly the supplyleads for the motor 20 enters the casing H at a terminal block 52 in itsside wall. 7

Electrical control means has been provided for the actuating motor 28such that operation of a manual switch serves to institute either anantenna-projection or antenna-retraction cycle of operation for themotor, as may be required, and which is automatically terminated at thecompletion of the desired movement of the extensible antenna.Furthermore, the controls are such that the usual on-off switch on theassociated radio set itself may be used to institute these cycles ofoperation so that the antenna is automatically projected into operativeposition whenever the radio set is turned on, and automatically drawn inwhen the radio set is turned ofi.

The wiring diagram for the control system noted above is shown in Fig.9. Upon reference to it, it will be seen that the conventional storagebattery for an automobile, indicated at 33, may constitute the source ofpower for both a radio receiving set M and the actuating motor 20 forthe antenna. The control system also includes a double-pole reversingrelay 4%: as well as up and down limit switches it and d1. Incidentally,the relay 55 is mounted in the casing l l on one end of the motor casing25 (see Fig. 4), while the limit switches 36, W are also mounted in thiscasing at the respective ends of the motor, the particular constructionof these switches being hereinafter described. The reversing relay 45comprises stationary contacts 58, 49 and 50, as well as movable contacts5| and 52. The movable contacts are carried by interconnected springfingers which also carry an armature 53 operated by an energizingwinding 54. When the relay is deenergized the movable contacts 5 l, 52are closed respectively against the stationary contacts 48, 69 and whenthe relay is energized the armature 53 ispulled down so that the movablecontacts engage respectively the stationary contacts 49 and 50,

With the control circuit connected as shown in Fig. 9, closure of themain on-ofi switch 55 of the radio set 44 connects the radio set to thebattery 43 and also energizes the relay winding 54 from this samebattery through conductors 56, 51. As heretofore noted such energizationof the relay causes its pairs of contacts til-49 and 5252 to close,thereby establishing an energizing circuit for the motor 20 (from thebattery 43 through 5622*5250.5846-59-2l 49-5l to ground) so that themotor rotates in a direction to feed the fiexible helix l9 upward andproject the wave-receiving structure I0.

When the latter is fully projected the up limit switch 46 isautomatically opened thereby interrupting the energizing circuit setforth above and stopping the motor.

Upon opening of the radio set on-off switch 55 the radio set is, ofcourse, disconnected from the battery 43 and the relay 45 issimultaneously deenergized. Such deenergization of the relay causes itscontacts 48, Si and 49, 52 to close thereby establishing an energizingcircuit for the motor 20 (from the battery 43 through 5622--52- 49-2l60-41-48-5l to ground). It will be observed that in this alternativeenergizing circuit for the motor, the field winding 2l'- is energizedwith a reversed polarity compared with that in the first instance notedso that the motor 20 operates in the reverse direction to draw theflexible helix IS in and thereby retract the telescoping antennasections. Upon completion of full retraction of the antenna the downlimit switch 41 opens, thereby interrupting the motor circuit previouslydescribed and stopping the motor. It should be particularly noted thatwhen the radio set is turned off neither the antenna motor 20 nor itsreversing relay 45 draw any current after the antenna is finallyretracted so that continued drain on the car battery, when the radio setis not in use, is ob'viated. Furthermore, the arrangement is such thatif the current supply lead to the radio set should be brokeninadvertently the relay 45 will be deenergized thereby causing theantenna to be drawn in automatically. In other words the system failssafe.

Turning now to the details of the limit switches 46, 41 (Figs. 4 and 5)it will be seen that a very simple and compact limit switch arrangementhas been provided especially adapted for use with a drive mechanism ofthe character set forth. With the exception of the shape of theinsulator bushings at their outer ends the two limit switches aresubstantially identical in construction and accordingly the samereference numbers have been used to designate identical parts, In thecase of the down limit switch 41, it comprises a metal tube or housing6| fixed to the motor casing 25 and axially alined with the motor shaft.In this tubular housing BI is slidably mounted an insulator bushing 62having a central opening through which the flexible shaft I9 is free topass. This opening is however sufiiciently small that the enlargement l4on the inner end of the rod l4 cannot pass through it but will abutagainst it and force the insulator bushing down from the position ofFig. 5 to that of Fig. 4 when the antenna is retracted. A helicalcompression spring 63 yieldably urges the slidable bushing 62 to theposition of Fig. 5 and in which position it abuts against a secondinsulator bushing 64 fixed in the outer end of the tubular housing 6|.The center opening in this latter bushing 64 is large enough to permitfree passage of the enlargement l4 on the rod I4.

The sliding bushing 62 has an outer end portion of reduced diameterwhich is encircled by brass ring 65 that constitutes a bridging contactfor the limit switch. Cooperating with this bridging contact ring aretwo resilient contact fingers 66. These contact fingers are mounted oninsulator blocks 61 clamped to the exterior of the tubular housing 6| bya strap 68 (see Fig. 7). It will be noted that the bridging contact ring65 is slightly larger in diameter than the opposed reduced end portionof the fixed bushing 64. Consequently when the ring 65 is thrustupwardly into its bridging position shown in Fig. 5 the contact fingers66 are spread apart slightly to insure a firm frictional grip of them onthe bridging ring so that an eifective elec trical contact will beestablished. When the sliding bushing 66 is moved down, however, so thatthe bridging ridge 65 disengages the fingers 56, the latter snap inagainst the reduced nose of the vfixed insulator 64. The latter is,however, sufiiciently large that the fingers are retained spread apartfar enough that there is no danger of their touching or short circuitingon the tubular housing 5| through whose apertured side walls theyproject.

From the foregoing it will be seen that'the "down" limit switch 41 ispositively actuated to its open position by the butt end of the rod l4when the antenna is fully retracted so as to stop the drive motor 20automatically at such a point. In connection with the operation of theswitch structure it has been found that a fairly strong compressionspring 63 should be utilized since a weak spring or none at all at thispoint permits sufllcient over-running of the parts, due to the momentumof the armature 22, that the helix I9 is likely to become jammed in thedrive bushing 28. The spring 63, which is sufficiently long and strongto prevent the sliding bushing 62 from going solid against the endbushing 30 on the motor shaft, prevents any such jamming however.

The up limit switch 46 is identical with the down limit switch describedabove except that at its outer end it has a stationary bushing 64 with athroat of somewhat different shapethan that of the bushing 64. In thecase of the latter its throat or center opening is of cylindrical formand its outer end is shaped to receive the antenna section H. In thecase of the bushing 64 of the up limit switch 46, however, the throat inthe bushing is flared outwardly in a funnel shape. The shape or thethroat serves to guide the helix l9 at a proper angle to coil downsmoothly in the take-up chamber 3|. Actuation of the up limit switch 46is accomplished by means of a bead or enlargement 69 on the helix I9(see Fig. 6) which is larger than the central hole through the slidablebushing 62 and thus serves to force this bushing upward into switch-openposition when it contacts it at the end of the extension travel for theantenna.

The operation of the apparatus will in general be clear from theforegoing. As a brief rsum of such operation it may be noted that toextend the antenna and condition the radio set for operation, it is onlynecessary to close the radio set on-ofl switch 55 (Fig. 5). Closure ofthis switch energizes the relay 45 and starts the motor 20 revolving sothat the wire helix I9 is screwed axially through it and the set oftelescoping elements l4 to I! fully distended. Upon completion of thisprojection of the antenna the up limit switch 45 opens therebydeenergizing the motor 20. At the same time the tail end of the helix l9pulls open the muting switch contacts 31, 38 thereby removing the groundconnection from the antenna so that the radio set is conditioned foroperation, this ground connection having previously muted the set duringthe operation of the motor 20 so that no unpleasant interference noiseswould be emitted from the receiver.

Upon turning off the radio set 44, the operator need only open the mainswitch 55, whereupon relay 45 drops out and the motor 20 is energizedfor rotation in the opposite direction. The motor thus draws in thehelix I9 feeding it into the take-up chamber 3| where it is smoothly andautomatically coiled down into the container. At the institution of thisfeeding of the helix into the chamber 3| its pull on the leaf spring 30is relieved so that the muting contacts 31, 38 close preparatory to thenext projection of the antenna. The contraction of the antenna continuesuntil the butt end of the rod I4 opens the down limit switch 41whereupon the motor 20 is deenergized leaving all of the circuits dead.It will thus be seen that the operation of the antenna is fullyautomatic and is controlled simply as an incident to turning on and oilthe radio set so that the operator need give it no special attentionwhatever.

The antenna apparatus described above is characterized by its lowcapacity coupling with ground. The best manually operated automobileradio antennas on the market today have a capacity coupling to ground ofabout 35 mmf. On the other hand th introduction of an electric drivingmotor or other power actuated mechanism of the antenna is likely, in theabsence of special precaution, to run this capacity coupling up to 500or 600 mmf. Tests on the present antenna structure have shown, however,that it has a capacity coupling of only 47 mmf. or, in other words, thesame order-of magnitude as that for an antenna having no power actuatingmeans whatever. A number of factors contribut to this low capacitycoupling in the present appara- I a smallpart of the helix remainsin'the chamher so that there is very little surface left for capacitycoupling to the chamber walls. Altogether a highly efficient combinationof elements has been achieved.

In Fig. 11 I have shown a wiring diagram for a modified form of acontrol circuit for an antenna apparatus of the general character setforth above but which is such that the antenna can be stopped at willduring its projection movement, thus making it possible for the operatorto extend the antenna to any length desired. Aside from the controlelements the only change in the apparatus required is that the lower endof the casing II be made in th form of an insulating cup 34, as; shownin Fig. 10, rather than in the form of a metal cup. Furthermore, thflexible shaft I9 is now anchored directly to thi insulator cup and aseparate muting or grounding switch for the antenna, in the form of arelay I 00 (Fig. 11) is used. Incidentally the tail end of the flexibleshaft I 9 is anchored in the cup 34 with the same initial curl as beforeso that it will coil down smoothly into this cup when the antenna isretracted. The control arrangement of Fig. 11 also illustrates the useof a reversible motor I20 which, though generally like the motor 20described above, has two separate field windings I 2| and I2l which arealternatively energized for opposite directions of motor rotation ratherthan a single winding whose polarity is reversed for reversal inrotation. Such a double winding tus. In analyzing these factors itshould be borne tively, and varies inversely with the length of air orother dielectric gap between such surfaces. When the present antenna isprojected for operation the only parts remaining within the groundedcasing II, which are at antenna potential or in other words arethemselves parts of the antenna, are the butt end portion of the tub I1and a portion :of the small diameter helix I9. These are both separatedfrom the grounded casing I I by quite a wide air gap, however, since thecasing is of substantially greater diameter than either of them.Furthermore, the helix I9, being of small diameter presents a minimum ofexternal area. The magnetic structur of the motor and its shaft are alsoat ground potential but they are close to only the short length of thehelix I9 which projects through them. Also, the

insulating sleeve 29 in the motor shaft is made a as thick as thedimensions of the associated parts will permit so as to give a maximumair gap between even this short length of the helix I9 and the groundedmotor parts. This insulating sleeve. 29 also forms a high resistancebarrier between the metal parts of the motor and the adjacent antennaelement, namely, the helix I9, so that the leakage path between them isof very high resistance. Another factor, heretofore noted, which verymarkedly reduces the capacity coupling is the elimination of any take-upreel for the helix I9. Upon reference to Fig. 6 it will be seen thatafter the helix has been fed out of the chamber 3| to its fully extendedposition only reversing motor may be controlled by a simpler form ofrelay shown as I45 in lieu of the more complicated double pole typeexemplified by the relay 45 above. Also included in the control systemof Fig. 11 is a push button switch IOI arranged to be held in openposition by releasable latch mechanism I02, the latch being released byenergization of an associated solenoid I03. Other parts of the controlsystem which are identical to those described above have been given thesame reference numerals.

Assuming that, in the system of Fig. 11, the antenna is retracted andthe radio set off, the operator closes the radio set on-off switch 55 toproject the antenna into operating position. Closure of this switchconnects the radio set 44 to the battery 43 and at the same timeconnects the main relay I45 to this battery. Energizationof this relayI45 causes its contacts I 45 to close and its normally closed contactsI45 to open. 'I'hereupon the motor I20 i energized (from the battery43through a circuit 43---I45*-I0I---I0Ii---4Ii-I2I -422 the antenna insome partially projected position he need merely depress the push buttonIOI, which may be located at some convenient joint as, for example, onthe dashboard of the car. When this push button switch is thus opened itis latched in open position by the latch I02. Since the .push buttonswitch IN is included in the energizing circuit for "up movement of themotor as well as in the energizing circuit for the relay I the motor andrelay I00 are both deenergized as soon as the push button switch IN isopened. The projection of the antenna is thus arrested and the mutingground connection for it opened.

In turning off the radio set 44 the operator opens the radio set switch55 whereupon the relay I is deenergized so that its contacts I 05 openand contacts 5 close. Closure of these latter contacts connects themotor I20 for rotation in a direction opposite to that heretoforedescribed (from the battery 43 through 5 IIIM"I03I22 to ground) so thatthe motor rotates to draw in the antenna. This rotation continues untilthe down limit switch 01 opens, thereby arresting further rotationof themotor. It will be observed that the energizing circuit just set forthfor the motor includes the solenoid I03 so that whenever the motorisenergized to draw in the antenna the latch I02 is automatically movedtoits disengaged position thus permitting the push button switch IM tosnap back out to its initial closed position, in the event that it hasbeen previously opened, thereby conditioning the circuit for asubsequent initiation of an antenna-projection cycle.

I claim as my invention:

1. An extensible radio antenna comprising, in combination, a pluralityof elongated metal antenna sections arranged in telescoping relation toeach other, at least the outer. one of said sections being of hollowtubular form, a transmission member extending longitudinally into theinterior of said outer section from the base end of the latter andoperatively connected to the innermost element of the series, saidtransmission member comprising a wire tightly spiraled in a long slenderhelix of substantially smaller diameter than the interior diameter ofsaid outer antenna section, an electric drive motor having a hollowshaft with interior screw threads, and means for restraining said helixagainst rotation, said helix of wire being threadably engaged by saidthreads in the motor shaft to screw the helix lengthwise and therebyproject or retract said telescoping sections upon rotation of saidmotor.

2. An extensible radio antenna comprising, in combination, a series oftelescoping antenna sections including a slender metal rod as theinnermost element of the series and a plurality of seamless metal tubestelescoped one over the other and over said rod, a transmission memberextending longitudinally into the interior of said series of antennasections from the base end of the outermost one and anchored to the buttend of said rod, said transmission member comprising a resilient andflexible wire tightly spiraled in a helix of a diameter substantiallythree times that of the wire itself, an electric drive motor having ahollow shaft with a tapped longitudinal bore, and means for anchoringsaid helix against rotation, said helix of wire being threaded in saidtapped shaft bore to effect a screwing of the helix lengthwise throughthe bore and thereby a projection or retraction of said telescopingantenna sections upon rotation of said motor.

3. In a radio antenna for an automobile installation or the like wherethe apparatus is subjected to strong vibration during use, thecombination of a series of tubular telescoping antenna sections, anelectric drive motor, and

means forming a drive connection between said motor and antenna sectionswhich is self-locking against a reverse action in which said motor isrotated by force applied to the antenna sections, said last named meanscomprising a hollow shaft for the motor presenting interior screwthreads in which a long, slender, and laterally flexible screw member,anchored against rotation and connected in driving relation with theantenna sections, is threaded for endwise movement.v through the sameupon rotation of the motor. i.

4. In a radio antenna, the combination with an extensible wave-receivingstructure including a closely spiraled helix of wire, and means forrestraining the helix against rotation, of an electric drive motortherefor having a hollow drive shaft through which said wire is led andpresenting interiorly located screw "threads mating with theconvolutions of said wire to feed the same axially through said shaftupon rotation of the latter.

5. In a radio antenna, the combination of an electric motor having anarmature shaft comprising a tubular metal jacket with a bushing ofinsulation fixed in it and an interiorly threaded metal bushing fixed insaid insulating bushing, an extensible wave-receiving structureincluding a closely spiraled helix of wire screwed in said threadedbushing, and means anchoring said helix against rotation, whereby saidhelix is shifted endwise by screw action upon rotation of the motorshaft. 6. A radio antenna comprising, in combination, an extensiblewave-receiving structure, means including an electric drive motor forprojecting and retracting said structure, said motor having a hollowdrive shaft presenting interior screw threads, and power transmissionmeans connecting said motor in driving relation with said extensiblestructure comprising a flexible helix of wire led through said shaft andscrewed in said threads.

7. In a device of the type described, the combination of a plurality ofelongated metal elements arranged in telescoping relation to each other,at least the outer one of said elements being of hollow tubular form, atransmission member extending longitudinally through the interior ofsaid outer element from the inner end of the latter and operativelyconnected to the innermost element of the series, said transmissionmember comprising a wire tightly spiraled in a helix of substantiallysmaller diameter than the interior diameter of said outer element withsuccessive convolutions of the wire abutting solidly against each otherand capable of transmitting both compression and tension forcesrequisite to project and retract the series of telescoping elementswithout substantial lateral distortion of said member, the ratio of thediameter of the wire to that of the helix which it forms beingapproximiately one to three, and means operatively connected to saidtransmission memher for coiling and uncoiling the portion thereofprojecting from the inner end of said outer element to retract andproject the telescoping elements.

8. In a device of the type described, the combination of a plurality ofseamless metal tubes telescoped one over the other, a slender metal rodtelescoped in the innermost tube, the outer ends of said tubes beingnecked in to a sufllciently small diameter to form a snug sliding fitwith the next adjacent telescoping element, a tightly said wireprojecting from the tubes for coiling and uncoillng the same to retractand project the telescoping elements.

9. In a device of the type described, the com- I bination of a pluralityof elongated metal elements arranged in telescoping relation to eachother, at least the outer one of said elements being of hollow tubularform, a transmission member extending longitudinally through theinterior of said outer element from the inner end of the latter andoperatively connected to the innermost element of the series, saidtransmission member comprising a wire tightly spiraled in a helix ofsubstantially smaller diameter than the interior diameter of said outerelement with successive convolutions of the wire abutting solidlyagainst each other and capable of transmitting both compression andtension forces requisite to project and retract the series oftelescoping elements without substantial lateral distortion of saidmember, the ratio of the diameter of the wire to that of the helix whichit forms being approximately one to three.

10. A radio antenna comprising, in combination, an extensiblewave-receiving structure including a long and closely spiraled wirehelix, an electric motor having a shaft with an elongated borepresenting interior screw threads, said helix being led through saidshaft bore and the convolutions of the helix mating with said threads, atake-up container presenting a generally cupshaped chamber to one end ofsaid shaft, said helix being led into said chamber, and means anchoringthe end of said helix in said chamber to -the container with the tailend portion of the helix permanently curled in a directioncircumferential of the interior of the chamber, whereby as the shaft isrotated to screw the helix into the chamber, the helix will coil down inthe chamber.

11. A radio antenna comprising, in combination, an extensiblewave-receiving structure including a long and closely spiraled wirehelix, an elongated cup-shaped sheet metal container, an electric motorhaving a stator and a rotor, said stator being fixed in the centralportion of said container and said rotor being carried by a hollow shaftextending longitudinally of said container, said shaft presentinginterior screw threads, said helix being led through said shaft with theconvolutions of the helix mating with said threads, said helix being ledinto a chamber defined between the closed end of the container and saidmotor, and means anchoring said end of the helix in said container inposition to curl the tail end portion of the helix in a directioncircumferential of the interior of said chamber, whereby as the shaft isrotated to screw the helix into the chamber the helix will automaticallycoil down snugly in the chamber.

' 12. A radio antenna comprising, in combination, an extensiblewave-receiving structure including a long and closely spiraled wirehelix, an electric motor having a shaft with a longitudinal borepresenting interior screw threads, said helix being led through saidshaft bore and the convolutions of the helix mating with said threads, atake-up container presenting a generally cupshaped chamber to one end ofsaid shaft, said helix being led into said chamber, means for anchoringthe end of said helix in said chamber to the container in position topermanently curl the tail end portion of the helix in a directioncircumferential of the interior of the chamber, and means located at theend of said shaft adjacent said chamber to form I an outwardly flaringfunnel-shaped guidethroat through which said helix passes.

13. A radio antenna apparatus of the ty e described comprising, incombination, a cylindrical metal casing having closed ends, an aperturein one of said casing ends, a tubular member insulatingly mounted insaid aperture and disposed coaxially with the casing, a plurality oftelescoping antenna sections projectibly mounted in said tubular member,an electric motor housed within the mid-portion of said casing andhaving a hollow shaft coaxial with the casing and alined with saidtubular member, said shaft presenting a set of interior screw threads, aflexible wire tightly spiraled in a helix of very small diameter ascompared to that of the casing, said helix being led through said hollowmotor shaft with the convolutions of the helix threaded in said screwthreads, the outer end of said helix being fixed to the innermost one ofsaicltelescoping antenna sections and the tail end of said helix beingled into the chamber formed between the motor and the closed end of thecontainer opposite said tubular member, said tail end of the helix beinganchored with a permanent curl in such portion of the helix in adirection circumferentially of the interior of the container.

14. The combination with an electric driving motor having a hollow shaftpresenting interior screw threads, and a long slender helix of flexiblewire threaded in said screw threads for movement axially through saidmotor shaft upon rotation of the latter, of a take-up container shaftthrough wihch said screw member is led and presenting interior screwthreads mating with said screw member, whereby said screw it member isthreaded axially through said shaft upon rotation of the latter, a pairof stationary tubular housings fixed to opposite ends of said motor andaxially alined with opposite ends of the motor shaft, insulator bushingsslidably mounted in respective ones of said housings and freelyencircling said screw member which is also led through said housings,limit-switch contacts on said bushings and cooperating stationarycontact elements, helical springs received in said housings andyieldably urging said bushings outward to engage said movable contactswith said stationary contacts, and means including abutments fixed tosaid screw member at spaced points along it for engaging correspondingones of said bushings to push the same inward in its housing against thebias of its abutting spring to open the associated set of contacts.

16. In a radio receiver antenna installation, the combination of anextensible antenna comprising a long flexible wire, a take-up containeradapted to receive the wire when coiled up in storage position, meansincluding an electric motor for feeding said wire out into extendedwavereceiving position or coiling it into said container, and meansincluding a normally closed switch for grounding said antenna wire whenclosed, said switch being connected to the inner end of said wire andpulled open thereby by the tension exerted on it by the wire when thelatter is in fully extended position.

17. In a radio receiver antenna installation, the combination of anextensible antenna comprising a long flexible wire, a take-up containeradapted to receive the wire when coiled up in storage position, meansincluding an electric motor for feeding said wire out into extendedwave-receiving position or coiling it into said container, a groundingswitch in said container comprising a stationary contact and a movablecontact on a leaf spring normally urging the movable contact intoengagement with said stationary contact, and the inner end 01' said wireleading into said container being fixed to said leaf spring, wherebywhen said wire is fed out 01' the container into wave-receiving positionsaid leaf spring will be pulled to open said contacts by the final tugof said wire as it reaches its limit position of extension.

18. In a radio antenna apparatus of the type described, the combinationof an electric drive motor having a hollow drive shaft presentinginterior screw threads, an extensible antenna comprising a long,slender, laterally flexible helix of wire led'through said motor shaftwith the convolutions of the helix threaded in said screw threads, acup-shaped take-up container presented to one end of said shaft with thetail end portion of said helix leading into it, an antenna groundingswitch comprising a leaf spring mounted in cantilever fashion to extenddiametrically across the inner face of the end wall of said container,and means anchoring the tail end of said helix to the free end portionof said spring at a point laterally displaced from the axis or saidshaft and with the fixed end portion of the helix extending transverselyacross said spring,

EDWARD L. BARRE'I'I.

